The present invention relates to a three-dimensional CAD (Computer Aided Design) system.
In the three-dimensional CAD system, basic configurations such as a rotary body, a protrusion, a hole, etc. (which are called features) are defined. Then, a user creates a final three-dimensional configuration by combining the defined basic configuration in a specified sequence. In the three-dimensional CAD system, such a method has hitherto been generally adopted. This type of CAD is known as a feature-based CAD system. FIGS. 17 and 18 show examples of the basic configurations described above. For example, a sweep may be defined as a basic configuration of a locus depicted when a two-dimensional graphic moves a predetermined distance. Further, the rotary body is a basic configuration of a locus depicted when the two-dimensional graphic rotates about a predetermined axis.
Moreover, in the three-dimensional CAD system, it might often happen that after the three-dimensional configuration has been temporarily generated and again changed. In such a case, it is required that a combination sequence of the already-added basic configuration be changed other than further adding the basic configuration to the final configuration. It is also required that the basic configuration be deleted and reproduced, and its shape and attribute be also changed.
For changing the three-dimensional configuration described above, the respective basic configurations for forming the three-dimensional configuration have hitherto been specified as follows:
(1) The basic configuration is specified by selecting the basic configuration appearing in the final three-dimensional configuration (such as pointing it with a mouse pointer, etc.).
(2) A feature tree for indicating a combination sequence of the basic configurations is displayed, and the basic configuration is specified by selecting the basic configuration expressed in the feature tree.
According to the method (1), however, there might be a case where all the basic configurations combined are invisible in the final three-dimensional configuration. For instance, if the final three-dimensional configuration is obtained by cutting a part of an in-the-making three-dimensional configuration, a basic configuration contained in the cut-off portion does not appear in the final three-dimensional configuration. It is therefore unfeasible to select the basic configuration contained in the cut-off portion.
Further, according to the method (2), the user is unable to grasp the in-the-making three-dimensional configuration and the basic configuration to be added. Hence, there might be induced a mis-operation such as changing the basic configuration that the user does not intend, and so forth.